A mail slot – American usage – or letterbox is a slot, usually horizontal but sometimes vertical, about 30 cm by 5 cm, cut through the middle or lower half of a front door. This style is almost universal in British homes and offices, but in the US is primarily found in older neighborhoods and on the east coast of the country. Most are covered by a flap on the outside for weatherproofing. The flap may be closed by gravity, or sprung to prevent it opening and closing noisily in the wind. Some letterboxes also have a second flap on the inside to offer further protection. There may also be a small cage or box mounted on the inside of the door to receive the delivered mail.
Wall-mounted or ‘attached’ mailboxes may also be used in place of mail slots, usually located close to the front door of the residence. They are common in urban and older suburban or high-density neighborhoods in North America. Attached mailboxes are less common in newer developments and in smaller towns and cities where mail is distributed through a combination of post office boxes and community mail stations.
Rural areas of North America utilize the curbside mailbox. It generally consists of a large metal box mounted on a support designed primarily to receive large quantities of incoming mail, often with an attached flag to signal the presence of outgoing mail to the mail carrier. In the U.S. and Canada, rural curbside postboxes may be found grouped together at property boundaries or road intersections.
A number of designs of mail boxes have been patented, particularly in the United States.
